This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2003-099360, filed on Mar. 30, 2001; the entire contents of which are incorporated herein by reference.
This invention relates to a magnetoresistance effect element; magnetic head and magnetic reproducing apparatus. More particularly, the invention relates to a magnetoresistance effect element configured to carry a sense current perpendicular to the film plane of a magnetoresistance effect film, and also to a magnetic head and a magnetic reproducing apparatus using the magnetoresistance effect element.
Discovery of giant magnetoresistance effect in a multi-layered structure of magnetic layers has triggered remarkable improvement of the function of magnetic devices, especially the function of magnetic heads. Especially, discovery of the giant magnetoresistance effect (GMR) by a spin valve (SV) film has brought about great technical development in the field of magnetic devices. A spin valve film includes a non-magnetic layer (called a spacer layer or non-magnetic intermediate layer) interposed between two metallic ferromagnetic layers to fix magnetization of one of the ferromagnetic layers (called a pinned layer or magnetically pinned layer) in one direction under a bias magnetic field from an anti-ferromagnetic layer or hard magnetic layer and to permit the other ferromagnetic layer (called a free layer of magnetically free layer) to incline its magnetization direction relative to the pinned layer in response to an external magnetic field such that a giant magnetoresistance can be obtained.
Among SV films of this type, a CPP (current-perpendicular-in-plane) type SV element configured to carry a current approximately perpendicular to the SV film plane exhibits a larger giant magnetoresistance effect than CIP (current-in-plane) type SV elements.
As one type of CPP elements, a TMR element using a tunneling magnetoresistance effect) film has been developed as well. Such a TMR film includes an insulating layer of Al2O3 as the spacer layer. The TMR film has the same layer configuration as that of the SV film from the viewpoint of the function.
The CPP magnetoresistance effect element using a magnetoresistance effect film (both a SV film and a magnetoresistance effect film are regarded herein to include a GMR film and a TMR film) not only exhibits a larger rate of MR change than CIP elements but also has the advantage that miniaturization of the element contributes to increasing the quantity of MR change because the resistance of the element relies on the element area.
This advantage is very useful in this era where magnetic devices are progressively miniaturized. For example, also regarding magnetic heads using SV films, which are under improvement of the recording density by approximately 60% a year, those using CPP magnetoresistance effect elements are regarded to be more and more hopeful along with progressive miniaturization of the reproducing head portions in accordance with improvements of the recording density.
Although, however, those CPP magnetoresistance effect elements have the above-mentioned advantages, they involve the problem about the scaling rule, which is peculiar to CPP elements, because the rate of MR change decreases when the element size approaches the mean free path of electrons. This phenomenon is not large as far as the element size is sufficiently large relative to the mean free path of electrons, but becomes serious together with onward miniaturization of the element.
That is, although conventional CPP magnetoresistance effect elements can cope with miniaturization to a certain extent, they are not readily applicable to superfine magnetic devices that will be desired in future, and could not perform their full function.
The present invention has been made taking those problems into account. It is therefore an object of the invention to provide a CPP magnetoresistance effect element that ensures a high rate of MR change and a large quantity of MR change without departing from the scaling rule even when its size is near the mean free path of electrons. A further object of the invention is to provide a magnetic device, especially a magnetoresistance type magnetic head, using the CPP magnetoresistance effect element, and a magnetic reproducing apparatus and a magnetic storage device using the magnetic device.
To accomplish the objects, a magnetoresistance effect element according to the first embodiment of the invention comprises:
a magnetoresistance effect film having a magnetically pinned layer which includes a ferromagnetic film whose magnetization direction is pinned substantially in one direction, a magnetically free layer which includes a ferromagnetic film whose magnetization direction varies with an external magnetic field, and a non-magnetic intermediate layer interposed between the magnetically pinned layer and the magnetically free layer;
a pair of electrodes electrically connected to the magnetoresistance effect film to carry a current in a direction approximately perpendicular to the film plane of the magnetoresistance effect film; and
sidewall layers formed at least on side surfaces of the magnetically pinned layer, the non-magnetic intermediate layer and the magnetically free layer of the magnetoresistance effect film.
The sidewall layer may be formed by, for example, oxidizing, nitrifying, fluoridating, carbonizing, sulfurating or boronizing the side surface of the magnetoresistance effect film.
Since the sidewall layer is stabilized more when crystallized, the above-summarized configuration produces the effect that oxygen, nitrogen, fluorine, carbon, sulfur or boron contained in the sidewall layer is unlikely to spread into the magnetoresistance effect film. Additionally, since the crystallized portion clearly defines the boundary between the sidewall layer and the magnetoresistance effect film and thereby makes a sharp potential profile at the boundary, there is also the effect that the specular reflection effect of conduction electrons of the sense current further increases. Since the increase of the specular reflection effect results in making the best use of the mean free path of electrons, degradation of the MR-changing rate is prevented.
That is, the sidewall layer made of a compound of an oxide, nitride, fluoride, carbide, boride or sulfide on the side surface of the magnetoresistance effect film produces the specular reflection effect of electrons. Additionally, it is possible to prevent a decrease of the MR-changing amount.
If the sidewall layer is in form of a compound phase containing, as a major component thereof, an oxide, fluoride, nitride, boride, carbide or sulfide of any one selected from the group consisting of B, Al, Si, Ge, W, Nb, Mo, P, V, Sb, Zr, Hf, Y, Ti, Ta, Zn, Pb, Cr, Sn, Ga, Cu and rare earth elements, then the potential profile at the boundary can be sharpened, and the specular reflection effect of electrons on the side surface of the magnetoresistance effect film can be enhanced.
If the side wall layer contains at least one kind of element selected from the group consisting of Fe, Co and Ni, and at least one kind of element selected from the group consisting of B, Al, Si, Ge, W, Nb, Mo, P, V, Sb, Hf, Zr, Y, Ti, Ta, Zn, Pb, Cr, Sn, Ga, N, O, F, S, C, Cu and rare earth elements, then the potential profile at the boundary can be sharpened, and the specular reflection effect of electrons on the side surface of the magnetoresistance effect film can be enhanced.
If the sidewall layer is in form of a mixture phase mixing an amorphous phase and a crystalline structure containing Fe, Co or Ni as a major component, its resistance can be increased, and simultaneously, spontaneous magnetization thereof by Fe, Co or Ni in the crystalline structure enhances the bias effect from the hard bias film and the anti-ferromagnetic bias film. For the purpose of enhancing the resistance of the sidewall layer, the crystal grain side of the crystalline portion had better be small, and the maximum grain size is preferably not larger than 20 nm. The ratio the crystalline structure occupies in the sidewall layer is preferably not more than 50% to ensure a high resistance. Therefore, the content of Fe, Co or Ni in the sidewall layer is preferably not more than 70 atomic %, and more preferably, not more than 50 atomic %. That content may be otherwise determined in case the crystalline structure is made of an oxide, fluoride, nitride, boride, carbide or sulfide.
If the sidewall layer includes an amorphous phase containing as its major component an oxide, fluoride, nitride, boride, carbide or sulfide of at least one kind of element selected from the group consisting of B, Al, Si, Ge, W, Nb, Mo, P, V, Sb, Hf, Y, Zr, Ti, Ta Zn, Pb, Cr, Sn, Ga and rare earth metals, diversion of the sense current from the side surface of the magnetoresistance effect film can be prevented.
In case the sidewall layer contains, as its major component, an oxide, fluoride, nitride, boride, carbide or sulfide of at least one kind of element selected from the group consisting of B, Al, Si, Ge, W, Nb, Mo, P, V, Sb, Hf, Y, Zr, Ti, Ta Zn, Pb, Cr, Sn, Ga and rare earth metals, the specular reflection effect at the side surface of the magnetoresistance effect film can be enhanced. In this case, if the sidewall layer is in form of a mixture of a crystalline structure and an amorphous phase, both an increase of the specular reflection effect by the crystalline phase and an increase of the resistance by the amorphous structure can be realized simultaneously.
The sidewall layer may contain as its major component an oxide, fluoride, nitride, boride, carbide or sulfide of at least one kind of element selected from the group consisting of Fe, Co., Ni, Mn, B, Al, Si, Ge, W, Nb, Mo, P, V, Sb, Hf, Zr, Ti, Ta, Zn, Pb, Cr, Sn, Ga and rare earth metals, and may be in form of a substantially amorphous phase.
Crystallization of the sidewall layer produces the effect that oxygen, nitrogen, fluorine, carbon, sulfur or boron contained in the sidewall layer is unlikely to spread into the magnetoresistance effect film. Additionally, since the crystallized portion clearly defines the boundary between the sidewall layer and the magnetoresistance effect film and thereby makes a sharp potential profile at the boundary, there is also the effect that the specular reflection effect of conduction electrons of the sense current further increases.
As a method of identifying a xe2x80x9ccrystalline phase,xe2x80x9d electron diffraction, for example, may be used. For example, if a diffraction spot having an orderly arrangement is observed in an electron diffraction image obtained through a transmission type electron microscope (TEM), the structure can be confirmed to be crystalline. More precisely, if a period suggesting an orderly arrangement is found in the diffraction intensity of the electron diffraction image, the structure can be confirmed to be crystalline. If equally spaced interstitial images, i.e. lattice images, derived from a certain plane orientation, or moire images caused by the overlap of lattices, are observed, then the structure is determined to be crystalline.
The xe2x80x9camorphous phasexe2x80x9d can be identified, for example, by the fact that no such periodicity is found in the electron diffraction, or the like.
Whether a structure is a xe2x80x9cmixture of an amorphous phase and a crystalline phasexe2x80x9d can be confirmed if both properties of a crystalline phase and an amorphous phase are observed depending on the location of the sample.
Whether it is magnetic or not can be confirmed by measuring magnetization of a thin film sample of the sidewall layer prepared by the same method. Alternatively, it can be known by measuring magnetization of a bulk sample or thin film sample of the same composition, based on a result of chemical composition analysis by EDX (energy dispersive X-ray spectroscopy), for example.
In any version of the magnetoresistance effect element according to the invention summarized above, thickness of the sidewall layer is preferably in the range from 0.5 nm to 10 nm. If the thickness is less than 0.5 nm, the sidewall layer cannot make a sharp potential profile at the boundary, and a sufficient effect of specular reflection cannot be obtained. Additionally, the sidewall layer is too thin to prevent diversion of the sense current.
On the other hand, if the thickness of the sidewall layer is 10 nm or more, effects of the use of the hard bias film and anti-ferromagnetic bias film for exerting a biasing effect to the free layer are seriously diluted due to magnetic decoupling, and it may result in deterioration of S/N ratio of the magnetoresistance head.
The magnetoresistance effect element according to the embodiment of the invention summarized above can be incorporated into a reproducing magnetic head to obtain a highly sensitive magnetic head.
The magnetoresistance head, thus obtained, can be mounted in a magnetic reproducing apparatus to enable stable reproduction of super-densely recorded information.
A magnetic storage device having a plurality of magnetoresistance effect elements according to any one of the above-summarized types is useful as MRAM (magnetic random access memory) that can magnetically rewrite information. That is, when the magnetoresistance effect element according to the embodiment of the invention is used in MRAM having no hard bias film or anti-ferromagnetic bias film, the sidewall layer having the specular reflection effect shows its effect.
As summarized above, according to the embodiment of the invention, since a CCP type magnetoresistance effect element has formed a sidewall layer on a side surface of the magnetoresistance effect film, high MR-changing rate and large MR-changing amount can be obtained even in a magnetoresistance effect element of a submicron size or a smaller size without departing from the scaling rule.
In addition to that, it is also possible to provide a magnetic head having high output power and high S/N, magnetic reproducing apparatus using same, and magnetic storage device using same. Thus the invention has remarkable industrial advantages.